A full length cDNA clone has been isolated from a human library. The messenger RNA derived from the gene is induced 20 to 80-fold upon stimulation of normal human lymphocytes with a variety of mitogens. The mRNA appears within two hours of growth stimulation and persists for at least 4 days. It appears to code either for a secreted protein or for a membrane protein. Because the mRNA is associated with growing human cells, mouse fibroblasts and mouse tissues, the data best fit a model in which the clone codes for a membrane protein required for growth.